1. Field of the Invention
The present invention relates generally to electronic ballasts for fluorescent lamps, and relates more particularly to electronic ballast controls that can prevent fluorescent light flashes.
2. Description of the Prior Art
Electronic ballasts for fluorescent lamps are well known, particularly those that operate with a switching half bridge. Such an electronic ballast is illustrated in U.S. Pat. No. 6,008,593 to International Rectifier Corporation. Electronic ballast controls have evolved to include dimming functions, and in particular substantially linear dimming control. One type of dimming control is illustrated in U.S. Pat. No. 6,008,593 to International Rectifier Corporation.
When fluorescent lamps are operated in a dimmed mode, the electronic ballast can cause problems during ignition of the fluorescent lamp at startup. During startup, the electronic ballast produces a high voltage to ignite the lamp. In the type of situation where a low light level is selected and the lamp is ignited, an undesirable flash across the lamp can occur because the time it takes for he lamp to first ignite at the maximum brightness level ant then transition to the final low dimming level is noticeable to the human eye. For this reason, it would be advantageous to prevent the fluorescent lamp from flashing during ignition and running.